    public class Person
    {
        // Field
        public string name;

        // Constructor that takes no arguments.
        public Person()
        {
            name = "unknown";
        }

        // Constructor that takes one argument.
        public Person(string nm)
        {
            name = nm;
        }

        // Method
        public void SetName(string newName)
        {
            name = newName;
        }
    }
    class TestPerson
    {
        static void Main()
        {
            // Call the constructor that has no parameters.
            Person person1 = new Person();
            Console.WriteLine(person1.name);

            person1.SetName("John Smith");
            Console.WriteLine(person1.name);

            // Call the constructor that has one parameter.
            Person person2 = new Person("Sarah Jones");
            Console.WriteLine(person2.name);

            // Keep the console window open in debug mode.
            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();
        }
    }
    // Output:
    // unknown
    // John Smith
    // Sarah Jones